Soil releasing textiles



United States Patent Office 3,521,993 Patented July 28, 1970 3,521,993SOIL RELEASIN G TEXTILES Ronald Swidler, Pasadena, Calif., Ray S. Smith,Greensa boro, N.C., and Harry A. Miller, Altavista, Va., assignors toBurlington Industries, Inc., Greensboro, N .C., a corporation ofDelaware N Drawing. Continuation-impart of application Ser. No. 645,599,June 13, 1967. This application Nov. 15, 1967, Ser. No. 683,139

Int. Cl. D06c 29/00 US. Cl. 8115.6 10 Claims ABSTRACT OF THE DISCLOSUREAn improved process for the treatment of textiles preferably to providedurable press and soil release properties. The fabrics are treated witha durable crease resin and a soil release polymer, in the presence of anaryl stearic acid, and cured. The soil release resin is one whichabsorbs at least five times its Weight of water when immersed in anaqueous detergent solution for 2 minutes at 140 F.

This is a continuation-in-part of prior application Ser. No. 645,599,filed June 13, 1967, now abandoned.

The present invention is concerned with the provision of resinorreactant-treated textiles or the like which possess improved soilreleasing properties.

The invention herein is particularly applicable to textiles of thedurable-press type, whether precured or postcured." As understood in theart, precured goods comprise fabrics which are cured before they areplaced in final form. Such fabrics are usually processed by impregnatingwith a water-soluble aminoplast resin precondensate or like reactant,followed by drying and curing before cutting, sewing and/or otherwiseputting the fabric into its final form. This technique may be used, forexample, in the preparation of durable press sheets, shirting materialor the like.

On the other hand, postcured textiles are those which are not cureduntil after they have been processed into final form, e.g. into agarment. In this case, the textile is impregnated with the resinprecondensate or reactant and dried without curing, the goods being thenput into the desired final form, e.g. by cutting and sewing into agarment and then pressing and curing to permanently fix the press. Thelatter approach, involving impregnation, drying without curing, garmentformation, pressing and curing, is described in US. Pat. 2,974,432 andrepresents one way of preparing the durable press garments which havebecome popular in recent years. Durable press products may also beobtained by partially precuring the fabric during the drying operationand/ or simultaneously pressing and curing. The invention herein may beused with any of these modifications, as well as with the moreconventional procedures for preparing precured or postcuredresin-treated fabrics.

One difliculty with conventional durable press fabrics, whether precuredor postcured, is their tendency to be stained by oil-borne and/or colorbearing materials including, e.g. salad oils, motor oil, butter, gravy,lipstick, hair oil and salad dressing, etc., as well as catsup, mustard,cranberry juice which might be considered water-borne and grass stains.This difliculty is at least partly due to the use of polyester fibers indurable press fabrics. Typically, polyester fibers are used togetherwith cellulosic fibers such as cotton, because the cellulosic can becross-linked with the resin to give the desired durable presscharacteristics but its tear strength is reduced by the process.Polyester fibers are rather strong and compensate for the loss ofstrength by the cellulosic. However, they are relatively sensitive tostains, particularly oil-borne stains, and when oily substances or colorbearing materials are taken up by them, as well as by the resin and anyother fibers, it is very difficult to remove them by laundering. Thestains can be removed by dry cleaning but this is expensive andundesirable, particularly since durable press fabrics are otherwise wellsuited for home laundering and an important advantage thereof is thatthey retain their shape through laundering and need little, if any,ironing.

Numerous proposals have been made to improve the soil releasingproperties of durable press fabrics, particularly with respect to stainsof the type referred to above. Some of these proposals are undesirablebecause they require more than a single washing of the fabric to removethe stains. One process, which gives effective soil release in a singlewashing, is described in the copending application of Hinton et al.,Ser. No. 604,649, filed Dec. 27, 1966, and a continuation-in-partthereof Ser. 'No. 681,092, filed Nov. 7, 1967, the subject matter ofwhich is incorporated herein by reference. According to said process,fabric which has previously been treated with textile resin or reactantis coated with a synthetic polymer, e.g. a copolymer of styrene andacrylic acid or ethyl acrylate and methacrylic acid of relatively highmolecular weight which is water insoluble but absorbs at least about550% by weight of water when immersed in an aqueous alkaline detergentsolution having a pH of at least about 8 for 2 minutes at F. Thisprocedure gives good soil releasing properties with respect to a widevariety of stains but it is limited to use with precured fabrics, i.e.fabric which has already been impregnated with resin, dried and cured. AsOil releasing effect can be obtained if treatment with the polymerprecedes application of the resin precondensate or the reactant of thedurable press type, but this undesirably affects the durable pressproperties. Ap plication of the soil release copolymer of Ser. No.604,649 to fabric containing the resin precondensate or reactant in theuncured state (i.e. postcured goods) is likewise undesirable. This is aserious limitation on the process of Ser. No. 604,649 since most durablepress garments are presently postcured. Then, too, application of theprocess to precured goods has the disadvantage of requiring additionalimpregnating and drying steps which increase process costs.

The principal object of the present invention is to provide a processfor improving the soil releasing properties of textiles, particularlydurable press fabric, whereby prior difficulties are obviated. A moreparticular object of the invention is to provide a process of the typeindicated which may be used with any type of durable press fabric, i.e.,whether precured or postcured. Another specific object of the inventionis to provide an improvement in the processing of durable press fabrics,as such, or in garment form, whereby application of the resinprecondensate or reactant used for durable press effects and thetreatment for improving soil releasing properties are combined tominimize the number of steps involved. Other objects will also beapparent from the following detailed description of the invention.

The success of the invention is based on the finding that aryl stearicacids, preferably monocarbocyclic aryl stearic acids and especiallyphenyl stearic acid are unexpectedly effective in improving the soilrelease properties of textiles. In a particularly preferred embodimentof the invention it has been found that conventional aminoplast resinprecondensates or other textile reactants and the waterabsorbing orswellable polymers of Ser. No. 604,649 may be applied simultaneously tothe fabric to obtain outstanding durable press effects and soil releaseproperties provided the treating bath also includes phenyl stearic acid.The manner in which the acid functions to make this possible is notunderstood. It appears that the acid may react or otherwise cooperatewith the aminoplast or textile reactant and the water-absorbing polymerto form a matrix polymer which gives the improved soil releaseproperties. Whatever the explanation, however, the acid functions insuch a way that the aminoplast precondensate or the like andwater-absorbing polymer are compatible with each other and are able toexert their respective functions Without interference to give thedesired durable press effects and optimum soil release characteristicsin the thus treated goods. The compatibility thus obtained means thatthe invention can be used whether the goods are to be precured orpostcured with considerable simplification in processing techniques. Forexample, it is only necessary to impregnate the fabric with a singlecomposition containing the precondensate, water-absorbing polymer andphenyl stearic acid, followed by drying, and precuring or postcuring asdesired. Accordingly, the present process makes it possible to avoid theextra impregnating and drying steps of prior procedures and theaccompanying expense. Furthermore, as opposed to presently knowntechniques, the invention gives not only a smooth drying fabric, butalso provides the important function of soil release together with animproved degree of static control.

The stearic acid-used herein may be represented by the followingformula:

wherein R is an aromatic group. Preferably R is phenyl or naphthylgroup, substituted optionally with alkyl, preferably lower alkyl groups,e.g. methyl. The aryl group also may be substituted with watersolubilizing groups such as hydroxy, carboxy and sulfate. These may makeit possible to omit an emulsifying agent from the treatment bath. Italso is to be appreciated that isomers of the compound as shown, withthe phenyl group disposed at any point from the second carbon in thestearic acid chain to the seventeenth, may be employed for presentpurposes. Phenyl stearic acid has been found particularly useful, butother aryl stearic acids, e.g. naphthyl stearic acid, xylyl stearicacid, and tolyl stearic acid, may also be used in lieu of, or inaddition to the phenyl stearic acid. However, the latter is definitelypreferred and gives the best results in terms of soil releasingproperties. Phenyl stearic acid also provides the best or most pleasinghand. Hydroxy substituted phenyl stearic acids are also useful, althoughthey tend to cause yellowing of goods.

The aryl stearic acid used herein may be prepared in conventionalmanner, eg, by alkylation of benzene or the like with oleic acid in thepresence of an acid activated clay or other acid catalyst.

As indicated, the water-absorbing polymer used herein may be any one ormore of those described in Ser. No. 604,649 and the aforesaidcontinuation-in-part as soil release agents. These may be defined aspolymers which absorb at least about five times the weight of waterunder alkaline conditions or, more specifically, at least about 550% byweight of water when immersed in an aqueous detergent solution for 2minutes at 140 F. (pH about 8-12). Preferably, this polymer is anaddition polymer of at least one ethylenically unsaturated monomerhaving one or more acid groups. Such monomers include, for example,acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acidand the like. Monomers which contain groups which readily hydrolyze inwater to form acid groups also may be used, for example maleicanhydride. Preferably, the acid groups are all carboxylic acid groups.However, it is possible for a portion of them to be phosphoric acid (POH or sulfonic acid (SO H) groups as well, by using monomers such asstyrene sulfonic acid and phosphoric acid ester of glycidyl allyl ether.The polymers may be manufactured by polymerizing the above monomers byany known means, for example with free radical or ionic catalysts.Alternatively, the polymers may be made by polymerizing an ethylenicallyunsaturated monomer such as acrylonitrile or an acrylic ester and thenhydrolyzing or otherwise modifying the resulting polymer to convert thenitrile, ester or other groups to acid groups.

The polymers may contain relatively small amounts of monomers which donot include acid groups, for example olefins, e.g. ethylene andpropylene, aromatic olefins such as styrene and various methyl styrenes,acrylic and methacrylic esters such as methyl methracrylate and ethylacrylate, dienes such as butadiene and isoprene, vinyl halides, e.g.vinyl chloride and vinylidene chloride, other acrylic monomers such asacrylamide and acrylonitrile, and the like. In general, the proportionof such non-acid monomers should not exceed about 60 mole percent andpreferably 40 mole percent. For maximum durability, it is preferred touse a system which leads to the crosslinking of the acrylic polymers,providing a matrix polymer with the other materials present.

Particularly useful materials for use herein as the water-absorbing orswellable component are: polyacrylic acid, acrylic acid or methacrylicacid copolymers for example copolymers of styrene and acrylic acid,copolymers of itaconic acid and acrylic acid; and copolymers of ethylacrylate and methacrylic acid; the copolymers of styrene, e.g. copolyersof styrene and maleic anhydride; and methacrylic acid and acrylic acidterpolymers such as terpolymers of methacrylic acid, butadiene andstyrene; and terpolymers of monomethyl itaconate, acrylic acid anditaconic acid.

Preferably the water-absorbing polymer is one which absorbs at leastabout 1000% by weight of water. This is evidenced by Very substantialswelling of the polymer although the polymer should not be soluble inalkaline solutions. The suitablility of a polymer for use herein can bereadily determined by measuring its water absorbing capacity orswellability. To do this, fabric treated with the polymer only isweighed, and the original weight of fabric is subtracted. The fabric isthen immersed in detergent solution for two minutes at 140 F., blotteddry with paper towels and then weighed. A correction is made for theliquid absorption by the fabric itself by repeating the procedure withuncoated fabric. The swelling is equal to:

weight gain in coating dry weigli of coating X A typical detergentsolution which may be used for this purpose is .15% TIDE detergent inwater. TIDE comprises sodium lauryl sulfate 16%, alkyl alcohol sulfate6%, sodium polyphosphate 30%, sodium pyrophosphate 17% and 31% sodiumsilicate and sodium sulfate combined.

The water absorbing (or swelling) characteristic of the soil releasepolymer is related to molecular weight. In general, low molecular weightpolymers of the type de scribed above are water soluble whereas highermolecular weight polymers are insoluble in water but will swell. For themost part, suitable polymers will have a number average molecular weightof 1,000 to 3,000,000, although this is subject to some variationprovided the desired degree of water absorption or swelling is realizedwithout dissolution of the polymer.

Another factor affecting the water absorbing property or swellability ofthe polymer is the degree of crosslinking therein. The polymers usedherein are essentially linear polymers. A certain degree ofcross-linking may be introduced into the polymers during subsequenttreatments. Although such crosslinking is not absolutely essential, itis desirable for durability. However, excessive crosslinking tends toconnect the polymer molecules into a rigid three dimensional networkwhich will not swell and this is not particularly useful for presentpurposes. Suitable crosslinking agents are formaldehyde, polyfunctionalalcohols, formaldehyde amine precOndensates,

polyfunctional epoxides, etc. These may be included, as desired, toimprove durability.

Any of the aminoplast resin precondensates or other textile reactantsconventionally employed for. imparting durable press effects may be usedherein. This includes formaldehyde and any of the water-solubleprecondensates of formaldehyde with such amino compounds as urea,thiourea, cyclic ethylene ureas (e.g. dimethylol cyclic ethylene urea ordimethylol dihydroxy cyclic ethylene urea), melamine, ethyl carbamate,urons, triazones and triazines. Blocked isocyanates may also beeffectively used.

Typically the invention is practiced by impregnating the fabric with anaqueous composition containing (1) the aminoplast resin precondensate orlike reactant, (2) the water absorbing, swellable polymer as describedabove and (3) phenyl stearic acid. Wetting agents, plasticizers,softeners and the like may be employed as desired in conventionalamounts. An appropriate catalyst for curing the aminoplast or likereactant should also be included and any of the standard catalysts maybe used for this purpose, the ultimate selection depending on such factors as whether the fabric is to be precured or postcured. Typicallysuitable catalysts include magnesium chloride or nitrate or zincchloride or nitrate; various amine hydrochlorides such as2-amino-2-methyl-l-propanol hydrochloride, or triethanolaminehydrochloride; and ammonium salts such as ammonium chloride tartarate,citrate, formate, oxalate, nitrate or ammonium ethyl phosphate orammonium dihydrogen phosphate or the like. These catalysts may becombined and/or catalyst modifiers may be added as necessary to achieveany desired effects, e.g. to increase or decrease catalyst activity.

Typically the composition used for impregnating the fabric (for example,by padding or spraying) will comprise, on a weight basis, from 5-20%aminoplast precondensate, usually -15%; 140% phenyl stearic acid,preferably 3-5 1-10% and preferably 2-5% soil releasing polymer; and0.12.5% catalyst, balance water with the optional addition of wettingagents, plasticizers, softeners and the like as noted above. It will berecognized, however, that other proportions can be used, the optimum inany particular situation depending upon other operating factors, e.g.the nature of the fabric and its intended use. Advantageously, thecomponents are simply added to water to make up the impregnatingcomposition although it is preferred to emulsify the phenyl stearic acidin a mixture of water and xylene (or toluene) before adding same to thecomposition.

The amount of the composition applied to the fabric can be widely variedand is also dependent on such factors as the nature and construction ofthe fabric, its intended use, etc. Usually, however, wet pickup Willfall in the range of 30-50% by weight of the fabric. This fabric is thendried, usually at 190-220 F. for 1-5 minutes, and cured at BOO-350 F.for 1-15 minutes. Precured goods are usually cured for from 1 to 3 or 5minutes and postcured goods are normally cured for somewhat longertimes, generally from 10 to minutes. The drying procedure provides adegree of partial cure, usually about and forms at least some crosslinking in the matrix polymer embodying the acid, the catalyst, thedurable press resin, and the soil releasing polymer, because theessential components have been found resistant to wash off where aplural bath technique is employed.

In the case of postcured goods, the dried fabric may be cut into desiredshape, sewn into a garment or other article, pressed on a hot head pressor the equivalent and then cured. Whether precured or postcured, goodsprocessed according to the invention demonstrate outstanding soilrelease and durable press properties as well as other essentialcharacteristics such as hand and antistatic properties. On laundering, asingle wash on a conventional home washing machine using builtdetergents is sufficient to completely remove stains caused bysubstances such as salad or cooking oils, motor oil, butter, lipstick,hair oil, salad dressings, etc. Frequently the aqueous detergent or soapsolutions have a pH of 7-12, although the invention may be useful withother soap or detergent solution. The phenyl stearic acid somehowfunctions, presumably as a result of the formation of the matrixpolymer, to permit the soil release polymer to absorb water and swell soas to facilitate removal of stains by the detergent while at the sametime avoiding undesirable inter-reactions between the polymer,aminoplast and/ or fabric which would prevent the aminoplast fromproviding permanent press eifects. It is completely surprising thatthese two effects can be obtained together in the manner indicated.

The invention may be used to improve the soil release properties of anytype of fabric, knitted, woven, or nonwoven, which is resin treated. Itis of particular advantage in the case of durable press fabricscomprising blends of polyester and cotton fibers since these areespecially susceptible to stains from oily substances. However, othertypes of fabrics made up entirely of natural or synthetic fibers, forexample polyester or 100% cotton, may also be effectively processed inthe manner described herein using phenyl stearic acid to obtain improvedsoil release properties. Such other fibers include, in addition topolyester and cotton, glass, wool, rayon, cellulose acetates,polyamines, acrylics, polyolefins, separately or in admixture. Othernontextile substrates may also be usefully processed according to theinvention where soil release is desired.

The invention is illustrated by the following examples wherein parts andpercentages are by weight unless otherwise indicated.

EXAMPLE 1 A woven 65/35 polyester/cotton fabric was padded with thefollowing formulation:

Percent Dihydroxy dimethylol ethylene urea (Reactant 183) 10 Phenylstearic acid (water/xylene emulsion) 5 Copolymer of 2.7 molesmethacrylic acid and 1 mole ethyl acrylate (molecular weight about800,000 to 1,500,000) 5 Ammonium chloride 0.4-0.5 Balance, water.

Citric acid also may be used as a catalyst.

The wet pickup was about 40-45% on the dry weight of the fabric. Thefabric was then dried at ZOO-220 F., for two minutes, cut, sewed into agarment leg, pressed on a hot head press at 300 F. (10 seconds) andpostcured at 325 F. for 10 minutes.

The thus processed garment leg was then tested for soiling by spottingwith various oily substances using the soil release test set forthbelow. The soil release was evaluated as Class 5, i.e. no visible oilstains remained, with only a single washing. The press was retained evenafter ten washings and other properties of the garment, e.g. softnessand hand, were also outstanding.

The soil release test utilized herein was as follows:

The cured specimen, after conditioning for an hour, is soiled indifferent areas with corn oil, mayonnaise, butter, lipstick, chocolatesyrup, coffee and hair oil. The soiled sample is given a single washingin a home laundry agitator type washing machine using a low sudsingdetergent (e.g. AD, pH about 10) in wash water at F. After washing for10 minutes, the sample is rinsed at 105 F., extracted and tumble driedat ISO- F. After conditioning, the sample is placed on a black surfaceunder a fluorescent light. The sample is visually rated under theseconditions with numerical ratings as follows:

Class 5--No staining Class 4Slight, but not appreciable staining 7 Class3Noticeable staining Class 2-Very noticeable staining Class l-Veryextreme staining EXAMPLE 2 Example 1 was repeated except that the fabricwas precured by curing in the fiat condition at 350 F. for minutes. Theresulting fabric remained wrinkle-free even after repeated washings andhad a rating of 5 on the soil release test.

EXAMPLE 3 Example 1 was repeated except that a copolymer of styrene (2.5parts) and acrylic acid parts), molecular weight of about 5,000 wasemployed in lieu of the copolymer used in Example 1. Essentially similarsoil release and durable press properties were obtained.

EXAMPLE 4 This example illustrates the application of the process to100% polyester fabric:

The fabric was impregnated in an aqueous composition containing 5%phenyl stearic acid, 5% of the methacrylic acid/ethyl acrylate copolymerof Example 1 and 10% blocked isocyanate (i.e. Nopco D612, apolyisocyanate blocked with phenol), balance water. Wet pickup was abouton the dry weight of the fabric.

The fabric was then dried at 220 F., pressed and cured at 325 F., theisocyanate becoming unblocked during the cure to set the press. Thepress was retained after repeated launderings and the soil test ratingwas 5.

It is to be noted that other available blocked isocyanates (monomeric orpolymeric) may be used in lieu of the Nopco 612 employed in the aboveformulation provided the unblocking thereof and reaction between theisocyanate and fabric readily occur at elevated temperatures which donot detrimentally affect the fabric (e.g. 275-350 F.). Typicallysuitable for use herein are the aliphatic or aromatic polyisocyanates,e.g. toluene dior tri-isocyanate, dimers or trimers thereof (such asshown in US. Pat. 2,801,244), hexamethylene diisocyanate or otheralkylene polyisocyanates, blocked with phenol. The phenol-blockedpolyisocyanates become unblocked at temperatures around 300 F., and atthis temperature, the released isocyanate effectively crosslinks orotherwise reacts with the fabric to give the desired durable presseffect.

While it is particularly advantageous, as exemplified above, to applythe phenyl stearic acid, aminoplast precondensate or other reactant andsoil release polymer from a single bath, the invention also contemplatesthe possibility of using a two bath technique wherein the phenyl stearicacid is first applied to the fabric, followed by drying and subsequentapplication of the aminoplast and soil release polymer. The two bathembodiment is illustrated by the following example:

EXAMPLE 5 A woven garment fabric made from yarn comprising 65%polyethylene terephthalate fibers and 35% cotton fibers (by weight) asin Example 1 was padded with an aqueous emulsion of 3% phenyl stearicacid. The fabric was heated at 325 F. for about one minute whereby thefabric was dried with apparent insolubilization of the phenyl stearicacid and the formation of a film thereof on the fabric.

The thus treated fabric was then impregnated with an aqueous solution ofthe following composition:

Percent Copolymer of about 2.7 moles of methacrylic acid and about 1mole ethyl acrylate (molecular weight about 300,000) 8 Di(hydroxymethyl)ethylene urea (Reactant 183) 10 Ammonium chloride catalyst .25 Polyvinylmethyl ether 1 Balance, water.

Wet pickup amounted to about 45% on the weight of the fabric.

The fabric was thereafter dried by heating at about 275 F. for 4-5minutes. This resulted in a partial precure (equivalent to about 30-40%fixed solids). The fabric was then cut and sewed into garments, pressedand then postcured in an oven at about 325 F. for about fifteen minutes.

The resulting garment was soft and otherwise demonstrated an excellenthand and possessed outstanding press retention even after repeatedwashings. When subjected to the soil release test referred to above, theoil stains were immediately and completely removed to give a rating of5.

It will be recognized that various modifications may be made in theinvention described herein. In its broadest aspects, the inventioncontemplates the treatment of textile materials with an aryl stearicacid, particularly phenyl stearic acid, as such or in combination with awaterabsorbing swellable polymer as described to improve soil releaseproperties whether or not durable press properties are involved. It isalso contemplated that the treatment with phenyl stearic acid accordingto the invention may be used to improve the soil release properties ofgarments or fabrics which have previously been given durable presstreatments. Other modifications will also be apparent. For example, thetreatment according to this invention can also be applied with usefuleffect to textile substrates generally, not requiring the presence ofcellulose, and to nontextile substrates, such as wood and concrete, torender them soil releasing. Hence, the scope of the invention is definedin the following claims wherein:

What we claim as new is:

1. A process for improving the soil releasing properties of a textilematerial which comprises impregnating the textile material with acomposition including an aryl stearic acid selected from the groupconsisting of aryl stearic acids having the formula wherein R is anaromatic group and isomers thereof wherein the aromatic group isdisposed at any point from the second to the seventeenth carbon atoms, adurable press textile reactant selected from the group consisting offormaldehydes, water-soluble precondensates of formaldehyde with aminocompounds and blocked isocyanates and a water-insoluble syntheticpolymer which absorbs at least five times its weight of water whenimmersed in an aqueous detergent solution for 2 minutes at 140 F., saidpolymer being an addition polymer of at least one ethylenicallyunsaturated monomer having one or more acid groups, and the thusimpregnated material is then dried and cured to obtain a product havingdurable press etfects as well as soil release properties.

2. A process according to claim 1 wherein said polymer is a methacrylicacid/ ethyl acrylate copolymer.

3. A process according to claim 1 wherein said textile material is afabric comprising polyester fibers.

4. A process according to claim 3 wherein said fabric is polyester.

5. A process according to claim 3 wherein said fabric comprises a blendof polyester and cellulosic fibers.

6. A process according to claim 3 wherein said fabric, after drying, iscut, made into a garment and pressed before curing.

7. A process according to claim 3 wherein the textile material is afabric comprising 100% polyester fibers and the textile reactant is ablocked isocyanate.

8. The product obtained according to claim 1.

9. A process according to claim 1 wherein the treatment comprisesimpregnating the textile material with a liquid composition containingsaid acid and drying, after which said textile is impregnated with anaqueous composition containing said durable press textile reactant, acatalyst OTHER REFERENCES for curing said reactant and said polymer,followed by Marsh crease Resistive Fabrics 133 134 (1962) drying andcuring.

10. The product obtained according to claim 9. GEORGE F, LESMES, p iExaminer References Cited 5 I. P. BRAMMER, Assistant Examiner UNITEDSTATES PATENTS US. Cl. X.R.

2,081,075 5/1937 Vobach 87-9 8115.5, 115.7, 116.2, 116.3, 116.4;117138.5; 260-21,

3,377,249 4/1968 Marco 8115.6 23, 29.4

22 UNITED s ATEs PATENT OFFICE CERTIFICATE OF CORRECTION Yatent No.3.521.993 Dated August 18, 1970 Inventor(s) George y It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

r Column 1, line 59, "and" should read --with--. Column 3. line 1 71,"substraction" should read --subtraction--. Column 5, line '11. "lever"should read --1eve1--. Column 5, Line 46, "preoid" should read--period--. Column 7, line 8, "7" should read --6--.

OCT 27 1970?;

Auest:

Edward M. Flew!!! If.

Attesting Officer wmrm E- W, JR.

domissiomr of Patents

